The present invention relates to a gas turbine engine of the type having rotating blades within a blade casing, and more particularly, to clearance control means for controlling the clearance between the rotating blades and the blade casing.
Modern gas turbine engines typically include a number of blade-to-blade casing interfaces. For example, a typical gas turbine engine for aircraft applications may include the following blade-to-blade casing interfaces: fan blades, compressor blades, high pressure turbine blades, and low pressure turbine blades. The clearance distance between the blades and the blade casings at such interfaces is a critical factor in the performance of such engines.
More particularly, unnecessarily large blade clearances are aerodynamically inefficient while small blade clearances often result in blade rub which may shorten engine life. The wide range of operation of such gas turbine engines, especially aircraft engines, results in significant variation of the clearance as the operating conditions vary. Thus, clearance control techniques have been developed which attempt to deal with this problem.
Although available clearance control techniques are acceptable for certain gas turbine engine applications, the use of such techniques often presents problems. These problems are due, in large part, to the wide range of operating conditions of such engines. In this connection, it is well known that the steady-state clearances of such engines are quite unlike their transient clearances. Thus, it has been found that conveniently available engine parameters, such as compressor speed or gas temperature, are not, by themselves, capable of establishing blade clearance control means which performs well over the wide range of operating conditions of such engines.
Accordingly, it is a general object of this invention to provide improved clearance control means for a gas turbine engine.
Another object of this invention is to provide such clearance control means which employs conveniently available engine parameters.
Another object of this invention is to provide such clearance control means which includes override means for accommodating transient operation.